Manufacture of permanent magnets



Patented Dec. 12, 1950 fSiTATiEZS PATENT F F-ICE 'Snciete 'Di Electro-chimie,

DElectro -Metall- -urgie et=des Acienies Electriques DUgine,'Paris, -France, acorporatiomof France No -Drawingi- Application February 7, 1947, Serial No. 'l27 ,'296. InfirancaFebruary-IS, 1946 4- Claims.

- This. invention :relatesr to the manufacturer of permanent magnets through agglomerating metallic powders;

Several'metho'dsare known at present for manufacturing; such: magnets. Thus, in the prior applications;Se1:.v Nos: 585;399 and 58-82766, now Patent No. 2,;4633413; means have been described which make it possible '130. obtairuby suchmethods, :permanent'magnetsw of? a {high quality;

It hasbeen explained more:particularly, .inzthe said: :patent applications; that metallic powders, the'ptarticlersizezof which is of thez'same order-as that-ofcolloidal powders, sshould be compressed; preferably inzaitcoldistateror withoutletting the temperature rise-highertthan 25'0" Ciandyin' any case, at a sufficientlylow temperature foravoiding a'sin't'ering or even a coalescence offthe parti-- cles. Such a coalescence was considered as capable of modifying and decreasing the-magnetic features o'f the finished magnet and :more particularly" of :reducing the coercive force it having been found that F high magnetic qualities could be obtained in the magnets only by using very fine-particle :powd'ers.

However" the soobtained magnets sometimes show av certain brittleness, particularly when the magnetic pieces are provided with sharp angles.

' The present-invention has"for its objectto'provide a method which makes it -possibleto considerably improve the-mechanical resistance of magnets obtained by the above mentioned methods without substantiallyreducingitheir magnetic features or evenwhile increasing the. latter. I-he said method consists in causing the magnet to undergo, during the agglomeration operation or after the latterya heating in aneutral'or reducing atmosphere to a temperature around 300- to 450C;

We .have discovered that, :when' thermagnets manufactured according to themethods described andi-claimed'in the above mentioned patent applications undergoatreatment at. about 300 C. in a neutral or reducing atmosphere, their mechanical properties are considerably improved-while their magnetioqualitiesiare notsubstantiallymeduced. We have also discovered that when the temperature of the heat-treatment is increased above the latter temperature, the mechanical properties are further increased in a very substantial proportion while, within a certain temperature interval, said variations are accompanied only by a very small reduction of the quality factor (max. BI-I) While aiverystrong increaseof the remanentinduction-may-be noted, together with a reduction oi-thecoercivaforce The'practice of the method according to the present invention thus makesitipossible to act upon the shape of the magnetisation curve and, accordingly, to manufacture a. magnet showing the magnetic features which are the :better adapted to the-use for which it is designed. In opposition with what happens when massive magnets undergo heattreatment,. the importance of the variations achieved through the .method according to the invention on magnets manufactured according to 'the" above =meritioned; patent applications is considerable. It was thus'possible to changethe magnetisation curve of a magnet, similar to that of: known..massive magnets based on nickel-aluminumyinto a curvezsimilarto thato'f a=massive magnet made of steel containing 35 per cent cobalt, this resultibeing obtained by the soleheattreatment forming the subject matter of the invention.

The followingare' afew-examples of working out of the method described above.

Example 'I' Br Ho max. BH

before treatment 6, 300 400 095x10 after treatment 6,600 390 106x10 Mechanical resistance was multiplied by 2.6 Shear strength of the angles was multiplied by 4.7. Dimensions of the magnets were reduced by l per cent.

Example II A similar magnet underwent a heat-treatment at 350 C. during one hour in an atmosphere of wet hydrogen; the modifications were the follow- 3:

. Br Hc max. BH

before treatment 6, 300 400 09x10 after treatment 7,300 335 1.1Xl

Traction strength was multiplied by 3.9. Shear strength of the angles was multiplied by 5.3. Dimensions of the magnet were reduced by 2.5 per cent.

Example III A similar magnet was heated during one hour at 395 C. in an atmosphere of wet hydrogen; the modifications were the following;

Br He max. BH 7 before treatment 6, 500 395 0.95X10 after treatment 8, 500 255 092x10 Mechanical resistance was multiplicdby 4.5. Shear strength of the angles was multiphed by 7. Dimensions of the magnet were reduced by 5.5 per cent.

Example IV A similar magnet was heated during one hour at 450 C. in an atmosphere of wet hydrogen; the modifications were the following:

Br He max. BH

before treatment 6, 400 395 0. 97 1u B after treatment 8, 700 190 0. 72x10 6 Mechanical resistance was multiplied by 10.5. Shear strength of the angles was multiplied by 18. Reduction of the dimensions of the magnet: 10 percent.

Example V max. BH a pparent Br Hc max. BH BIXHC density before treatment 7, 070 513 L54 10 6 0.425 4.45 after treatment... 8, 100 355 l. 3l 10 6 0. 456 4. 48

The shear strength of the angles was multiplied by 3.

Example VI T similar magnet was heated during one hour at 480 C. in hydrogen; it underwent the following modifications:

max. BH a pparent Br Hc max. BH BTXHC density before treatment- 5, 670 517 1. 12x10 0.382 4. 28 after treatment.-. 6, 850 347 0.975X 0. 410 4. 53

Shear strength of the angles was multiplied by 7.5.

One considerable practical interest of the invention consists in the fact that magnets treated according to the above described method may advantageously be used in the manufacture of modern type electricity meters because of their magnetic features as well as of their mechanical properties and may be placed among the best magnets available for wide sale meters. The method makes it possible to manufacture magnets of the small air-gap type without any polar masses or field closing plates, said type being frequently used in the manufacture of meters.

What I claim is:

1. In the treatment of permanent magnets obtained by agglomerating metallic powder, the rains of which are uninsulated and have dimensions of the order of those of colloidal particles, the step consisting in heating said permanent magnets in a non-oxidizing atmosphere within the range of about 300 C.-480 C. at such temperature as increases the remanent induction,.decreases the coercive force and at least maintains the product of both said factors.

2. In the treatment of permanent magnets obtained by agglomerating metallic powder, the grains of which are uninsulated and have dimensions of the order of those of colloidal particles, the step consisting in heating said permanent magnets in a reducing atmosphere within the range of about 300 C.-480 C. at such temperature as increases the remanent induction, decreases the coercive force and at least maintains the product of both said factors.

3. In the treatment of permanent magnets obtained by agglomerating metallic powder, the grains of which are uninsulated and have dimensions of the order of those of colloidal particles, the step consisting in heating said permanent magnets in a non-oxidizing atmosphere during agglomeration, said heating being within the range of about 300 C.-480 C. at such temperature as increases the remanent induction, decreases the coercive force and at least maintains the product of both said factors.

4. In the treatment of permanent magnets obtained by agglomerating metallic powder, the grains of which are uninsulated and have dimensions of the order of those of colloidal particles, the step consisting in heating said permanent magnets in a non-oxidizing atmosphere after agglomeration, said heating being within the range of about 300 C.-480 C. at such temperature as increases the remanent induction, decreases the coercive force and at least maintains the product of both said factors.

CHARLES MARQUAIRE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,669,643 Andrews et a1 May 15, 1928 1,840,352 Elmen Jan. 12, 1932 1,359,067 Beath May 17, 1932 2,298,885 Hull Oct. 13, 1942 FOREIGN PATENTS Number Country Date 590,392 Great Britain July 16, 1947 

1. IN THE TREATMENT OF PERMANENT MAGNETS OBTAINED BY AGGLOMERATING METALIC POWDER, THE GRAINS OF WHICH ARE UNINSULATED AND HAVE DIMENSIONS OF THE ORDER OF THOSE OF COLLOIDAL PARTICLES, THE STEP CONSISTING IN HEATING SAID PERMANENT MAGNETS INA NON-OXIDIZING ATMOSPHERE WITHIN THE RANGE OF ABOUT 300* C.-480*C. AT SUCH TEMPERATURE AS INCREASES THE REMANENT INDUCTION, DECREASES THE COERCIVE FORCE AND AT LEAST MAINTAINS THE PRODUCT OF BOTH SAID FACTORS. 